U.S. Pat. No. 3,960,531 describes a machine comprising a first plate for supporting a first optical fiber and equipped with means for translation parallel to the axis of the fiber, a second plate for supporting a second optical fiber and equipped with means for horizontal and vertical translation perpendicular to the axis of the fibers, a microscope for observing the ends of the optical fibers while their axes are being aligned by manual displacement of the plates, a moving wedge for marking a welding plane by the wedge abutting against the end of one of the fibers, and two electrodes for welding the ends of the fibers in the welding plane.
Such a machine is only applicable to low accuracy end-to-end welding of optical fibers, eg. for multimode fibers having a core diameter of about 100 microns.
The machine is not suitable for the kind of accuracy required to minimize light losses due welding nor is it suitable under any circumstances for monomode fibers which have a core diameter of a few microns only.
It is for such reasons that Research Disclosure No. 21643, April 1982 describes an automatic machine for positioning optical fibers, in particular for welding, along three orthogonal axes by means of a TV camera controlling a microprocessor. However, such a machine is very complex and expensive.
Preferred embodiments of the present invention provide an automatic machine for end-to-end welding of optical fibers with the axes of the fibers being aligned with great accuracy, eg. about 1/10-th of a micron. The machine can also reduce welding defects. Furthermore, alignment is performed rapidly without the need for operator dexterity, the heating of the fiber ends during welding can be closely controlled, and various welding cycles can be reproduced at will.